<svg xmlns="http://www.w3.org/2000/svg" version="1.1"
     width="100" height="100">
  <defs>
    <style>
      #myRect {
        animation-duration: 0.1s;
        animation-name: fade;
        animation-fill-mode: forwards;
      }

      @keyframes fade {
          0% { fill-opacity: 0 }
          100% { fill-opacity: 1 }
      }
    </style>
  </defs>
  <rect width="100%" height="100%" fill="red"/>
  <rect id="myRect" width="100%" height="100%" fill="lime" fill-opacity="0"/>
</svg>
